In the 1990s, the practical application of an MR (Magneto-Resistive effect) head and a GMR (Giant Magneto-Resistive effect) head triggers a dramatic increase in a recording density and a recording capacity of an HDD (Hard Disk Drive). However, since the beginning of the 2000s, a problem of thermal fluctuation of a magnetic recording medium is exposed, and therefore, a rate of increase in the recording density temporarily slows down. Still, recently, the HDD recording density has been increasing about 40% per annum, as the perpendicular magnetic recording more advantageous, in principle, for high-density recording than longitudinal magnetic recording was put into practical use in 2005.
In the latest recording density demonstration experiment, a level more than 400 Gbits/inch2 has been achieved. If the progress steadily continues, the recording density of 1 Tbits/inch2 is expected to be realized around the year 2012. However, the realization of such a high recording density is considered not easy even by using a perpendicular magnetic recording method, because the problem of thermal fluctuation is exposed again.
As a recording method to solve the above problem, a “high-frequency assisted magnetic recording method” has been suggested. In the high-frequency assisted magnetic recording method, a high-frequency magnetic field at a frequency in the neighborhood of the resonant frequency of a magnetic recording medium, which is sufficiently higher than the recording signal frequency, is locally applied to the magnetic recording medium. As a result, the magnetic recording medium resonates, and the coercivity (Hc) of the magnetic recording medium subjected to the application of the high-frequency magnetic field is reduced to not more than half the original value. Thus, the high high-frequency magnetic field is overlapped with the recording magnetic field, whereby magnetic recording on a magnetic recording medium having a higher coercivity (Hc) and a higher magnetic anisotropy energy (Ku) is allowed. However, it is difficult to efficiently apply the high-frequency magnetic field in the high-density recording.